Extraordinary boundary morphologies of large-scale ordered domains of spheres in thin films of a narrowly dispersed diblock copolymer via thermodynamic control

Abstract

Long-range ordering of body centered cubic (BCC) spheres and various extraordinary morphologies at the boundaries of the adjacent orderly oriented domains are observed in thermally annealed thin films of a series of specific narrowly dispersed diblock copolymers, poly(dimethylsiloxane)-b-poly{2,5-bis[(4-butoxyphenyl)oxycarbonylstyrene} (PDMS-b-PBPCS, DB). The series of asymmetrical DB block copolymers (BCPs) with volume fractions of PDMS (f_PDMS's) from 10% to 23% self-assemble into thermodynamically stable body centered cubic (BCC) nanostructures in bulk at ambient temperature after thermal annealing. The thin films of these BCPs with a relatively large film thickness on a carbon-film coated substrate are annealed in a vacuum at 180 °C for 3 days and are characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). For all thin films of these BCPs, micrometer-scale domains with a rectangular unit cell similar to the projection of the BCC lattice along the [110] direction to the substrate are observed. And the XPS results indicate that the surface layers of the thin films are composed of both PDMS and PBPCS blocks. For the thin films of the BCPs with f_PDMS values of 10% and 13%, the neighboring [110]-oriented BCC domains match well with each other, and the boundaries are defect-free. For the thin film of the BCP with a f_PDMS value of 23%, the PDMS spheres in the [110]-oriented BCC domains in the TEM micrograph are overlapped with each other, and interesting morphologies including defect-free interfaces, interfaces with line defects, and domains with defects and local ordering are observed at the boundaries of the neighboring [110]-oriented domains.